JPS62288339A - Air-fuel ratio control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To correct a slippage of a base air-fuel ratio, by correcting a reference value for air-fuel ratio control as set according to an engine load with a deviation between an output value of an O2 sensor and a target value, and correcting a unit proportional quantity when a correction value indicative of an error in the reference value is not less than a predetermined value. CONSTITUTION:A control circuit 20 reads a reference value for air-fuel ratio control from a data map according to an engine speed from a crank angle sensor 11 and an intake absolute pressure from an intake absolute pressure sensor 10 both relating to an engine load. When it is determined that air-fuel ratio feedback control conditions are satisfied from the intake absolute pressure, cooling water temperature, vehicle speed and engine speed, an integral term and a proportional term for feedback controlling a secondary air control valve 9 acoording to the engine speed and intake absolute pressure are calculated. Further, a present correction value of the reference value is calculated from a previous correction value and the integral term or the proportional term. When the present correction value becomes a predetermined value or more, or becomes a predetermined value or less, it is determined that a slippage of a base air-fuel ratio in a carburetor 3 has occurred, and a unit proportional quantity and a unit integral quantity are therefore corrected.

Description

[Detailed description of the invention] 3. Detailed description of the invention Technique Jzu Kuno The present invention relates to an air-fuel ratio control method for an internal combustion engine.

In order to purify the exhaust gas of internal combustion engines and improve fuel efficiency, the oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor, and the air-fuel ratio of the mixture supplied to the engine is adjusted according to the output level of the oxygen concentration sensor. Air-fuel ratio control devices that perform feedback control to a target air-fuel ratio are known (for example,
-3533@publication).

In such an air-fuel ratio control device, a reference value for air-fuel ratio control is set according to a plurality of engine operating parameters related to engine load, and the output value of an exhaust component concentration sensor such as an oxygen concentration sensor and a target are set for each predetermined circle II. The output value is determined by comparing the target value corresponding to the air-fuel ratio, determining the air-fuel ratio correction value according to the comparison result, and correcting the reference value with the air-fuel ratio correction value, and adjusting the air-fuel ratio according to the output value. The opening degree of the regulating solenoid valve is controlled. The air-fuel ratio correction value is, for example, a proportional amount and an integral amount determined by PI (proportional-integral) control according to the comparison result between the output value of the exhaust component concentration sensor and the target value, or a proportional amount and an integral amount determined by PI (proportional-integral) control only. Consists of integral quantities.

By the way, it is common for the pace air-fuel ratio of the carburetor to deviate from a predetermined value due to aging or deterioration of the carburetor, causing the set reference value to no longer correspond to the target air-fuel ratio and resulting in an error. be.

However, if the error in the M unit price becomes larger than a predetermined value, it becomes impossible to control the air-fuel ratio of the air-fuel mixture supplied to the engine to the target air-fuel ratio with high precision using air-fuel ratio feedback control, and good exhaust purification performance becomes impossible. There was a problem that it could not be obtained.

! SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an air-fuel ratio control method that can obtain good exhaust purification performance even if the error in the reference value becomes larger than a predetermined value.

The air-fuel ratio control method of the present invention is characterized in that when the correction value representing the error of base tP, 11 is calculated, the unit proportional amount or unit integral amount of the air-fuel ratio correction value is corrected according to the magnitude of the correction value. It is said that

X-Rin Ichidan Embodiments of the present invention will be described below with reference to the drawings.

In the air-fuel ratio control device of the intake secondary air supply system for a torpedo internal combustion engine to which the air-fuel ratio control method of the present invention is applied as shown in FIG. The air is then supplied to the engine 5 via the intake manifold 4.

The carburetor 3 is provided with a throttle valve 6, and a venturi 7 is formed upstream of the throttle valve 6.

The intake manifold 4 and the vicinity of the air discharge port of the air cleaner 2 are communicated through an intake secondary air supply passage 8.

A linear solenoid valve 9 is provided in the intake secondary air supply passage 8 . The opening degree of the solenoid valve 9 changes in proportion to the Ti flow value supplied to the solenoid 9a.

On the other hand, 10 is an absolute pressure sensor installed in the intake manifold 4 and generates an output at a level corresponding to the absolute pressure inside the intake manifold 4, and 11 generates a pulse in accordance with the rotation of the crankshaft (not shown) of the engine 5. 12 is a cooling water temperature sensor that generates an output at a level corresponding to the cooling water temperature of the engine 5; 14 is an oxygen sensor installed in the exhaust manifold 15 of the engine 5 and generates an output according to the oxygen concentration in the exhaust gas. It is a concentration sensor. A catalytic converter 33 is provided in the exhaust manifold 15 downstream of the oxygen concentration sensor 14 in order to promote reduction of harmful components in the exhaust gas. Linear type solenoid valve 9
, absolute pressure sensor 10 , crank angle sensor 11 , water temperature sensor 12 , and oxygen concentration sensor 14 are connected to a control circuit 20 .

Further connected to the control circuit 20 are a vehicle speed sensor 16 that generates an output level that corresponds to the speed of the vehicle, and a throttle valve opening sensor 17 that is comprised of a potentiometer and generates an output level that corresponds to the opening degree of the throttle valve 6. has been done.

The control circuit 20 includes an absolute pressure sensor 10, as shown in FIG.
Water temperature sensor 12, oxygen concentration sensor 14, vehicle speed sensor 16
and a level conversion circuit 21 that converts each output level of the throttle valve opening sensor 17, a multiplexer 22 that selectively outputs one of the sensor outputs that have passed through the level conversion circuit 21, and a signal output from the multiplexer 22. an A/D converter 23 that converts the output signal of the crank angle sensor 11 into a digital signal, a waveform shaping circuit 24 that shapes the waveform of the output signal of the crank angle sensor 11, and a TDC that is output as a pulse from the waveform shaping circuit 24.
A clock pulse generation circuit (not shown) determines the signal generation interval.
A counter 25 that measures the number of clock pulses output from the controller, a drive circuit 28 that drives the solenoid valve 9, a CPU (central processing circuit) 29 that performs digital calculations according to the program, and various processing programs and data are written in advance. It consists of a ROM 30 and a RAM 31. The solenoid 9a of the electromagnetic valve 9 is connected in series with a drive transistor and a current detection resistor (both not shown) of a drive circuit 28, and a power supply voltage is supplied across the series circuit. The multiplexer 22, A/D converter 23, counter 25, drive circuit 28, CPU 29, ROM 30, and RAM 31 are connected to each other by an input/output bus 32.

In this configuration, the A/D converter 23 selectively transmits information on the absolute pressure in the intake manifold 4, the cooling water temperature, the oxygen concentration in the exhaust gas, the vehicle speed, and the throttle valve opening, and the counter 25 selectively transmits information on the engine rotation. Information representing the numbers is supplied to the CPU 29 via an input/output bus 32, respectively. The CPU 29 is configured to generate an internal interrupt signal every predetermined period T+ (for example, 5 m5ec) as described later, and in response to the interrupt signal, an output value Tour representing the value of the current supplied to the solenoid 9a of the electromagnetic valve 9 is generated. is calculated as data, and the calculated output value TOLI is supplied to the drive circuit 28. Drive circuit 2
8 is the current value flowing through the solenoid 9a which is the output 1ifiTo
The W flow value flowing through the solenoid 9a is controlled in a closed loop so that the value corresponds to LJT.

Next, the operation of such an air-fuel ratio control device is shown in FIG.
A detailed explanation will be given according to an operation flow diagram of the PU 29.

As shown in FIG. 3, in the A/F routine, the GPtJ 29 first sets a reference value D[3ASE representing the reference current value to be supplied to the solenoid valve 9 every time an interrupt signal is generated (step 51). As shown in FIG. 4, the reference value DBAS, which is determined from the intake manifold absolute pressure PBA and the engine speed Ne, is stored in the ROM 30 in advance as a DOASE data map, so the CPU 29 uses the absolute pressure PE.
Read A and the engine speed Ne, and set the reference value Do A S E corresponding to each read value.
Search from the data map. After setting the reference (shift 1) 8ASE, it is determined whether the driving condition B of the vehicle (including the engine driving condition) satisfies the air-fuel ratio feedback (F/B) control conditions (step 52). This determination is determined from the intake manifold absolute pressure Pa A N cooling water @ TW, vehicle speed ■, and engine rotation speed Ne. For example, it is assumed that the air-fuel ratio feedback control condition is not satisfied at low vehicle speeds and low cooling water temperatures. . Here, if it is determined that the air-fuel ratio feedback control conditions are not satisfied, the reference value DBASE is multiplied by the correction w1) (rer and the calculated value is set as the output value ToUT (step 53).
31, the correction fn K ref for each region corresponding to the intake manifold absolute pressure PBA and engine speed Ne is written as a Kref data map as shown in FIG. The correction value Krer corresponding to the number Ne is searched from the Krer data map and used to calculate the output value TauT.

On the other hand, if it is determined that the air-fuel ratio feedback control conditions are satisfied, the internal timer counter A of CPLJ29
It is determined whether the counting time (not shown) has elapsed by a predetermined time Δtl (step 56). The predetermined time Δt1 corresponds to a response delay time from when the intake secondary air is supplied until the result is detected by the oxygen concentration sensor 14 as a change in the oxygen concentration in the exhaust gas. When a predetermined time Δt1 has elapsed since the time counter A was reset and started counting, the time counter A is reset and starts counting from the initial value (step 57).

That is, by executing step 57, the time counter A
After starting counting from the initial value, it is determined in step 56 whether or not a predetermined time Δt1 has elapsed. When the time counter A starts counting the predetermined time Δt1 in this way, it is determined from the oxygen concentration information whether the output value LO2 of the oxygen concentration sensor 14 is larger than the target value L ref corresponding to the target air-fuel ratio. (Step 58). That is, it is determined whether the air-fuel ratio of the air-fuel mixture supplied to the engine 5 is leaner than the target air-fuel ratio. If Lo2>Lref, the air-fuel ratio is leaner than the target air-fuel ratio, so it is determined whether the air-fuel ratio flag FAF representing the determination result of the previous step 58 is "1" (step 59). If FA F = 0, it is determined that the previous air-fuel ratio was rich and the ratio has been further reversed from rich, so step 60 is performed to calculate the proportional subtraction value PL.
). The subtraction value PL is obtained by multiplying a constant + (>1) by an integral subtraction value IL (described later) (K+·IL). After calculating the subtraction value PL, the air-fuel ratio correction value l0LJT that has already been calculated by executing this A/F routine
is read from the memory image ffa+ of the RAM 31, the subtraction value PL is subtracted from the read correction value 10LJT, and the calculated value is set as a new correction value 10UT and written to the memory image Ra1 of the RAM 31 (step 61). FA F = 1
If so, since it was determined that the air-fuel ratio was lean last time as well, the integral subtraction value IL is calculated (step 62). Subtraction value [
The difference is obtained by multiplying a constant by 2, the engine speed Ne, and the absolute pressure PBA (K2·Ne-PB^), and is made to depend on the intake air amount of the engine 5. After calculating the subtraction value IL, the correction 1fllouv already calculated by executing this A/F routine is read from the storage location a1 of the RAM 31, and the read correction value l0UT is
Subtract the subtraction value ■ from and use the calculated value as the new correction 1f
fIlouT and writes it into the memory image @at of the RAM 31 (step 63). After calculating the correction value 1 OLI in step 61 or 63, the 7-lag FAF is set to 1" to indicate that the air-fuel ratio is lean. In step 64), the reference value DBA set in step 51 is set.
The air-fuel ratio/correction value Iout is added to SE, and the addition result is set as the output value To LJ T (step 65). On the other hand, if LO2≦L ref in step 58, the air-fuel ratio is richer than the target air-fuel ratio, so the air-fuel ratio flag F
Determine whether AF is "0" (step 66)
. If it is FAF-1, it is determined that the previous air-fuel ratio was lean, and the ratio has been reversed from lean to rich, so a proportional addition value PR is calculated (step 67). The added value PR is 3 (>
1) and the integral addition value IR to be described later are multiplied together m (K3
・IR).

After calculating the additional value PR, the correction value four that has already been calculated by executing this A/F routine is read from the storage location a1 of the RAM 31, and the read correction value four is
and the addition n value PR, and the calculated value is set as a new correction value 1.
0LJT and written into the memory image 1a+ of the RAM 31 (step 68). In step 66 FA F =
If it is O, it was determined that the air-fuel ratio was rich last time as well, so an integral addition value IR is calculated (step 69). Addition value I
R is obtained by multiplying the constant by 4 (≠ by 2), the engine speed Ne and the absolute pressure P8A by n (K4 ・Ne - P6A), and is made to depend on the intake air amount of the engine 5. . After calculating the additional value IR, use the correction value 10U already calculated by executing the A/F routine as RA.
Read from the memory image 11a+ of M31, add the added value IR to the read correction value 10LJT, set the calculated value as a new correction value 10LJT, and write it to the memory image [a+ of the RAM 31 (step 70). After calculating the correction value 10UT in step 68 or 70, the flag FAF is set to "0" to indicate that the air-fuel ratio is rich (step 71), and the correction value Krer is calculated (step 7).
2). The correction value Krar is Kref−α10U+(1
-α)·KrefI)I. Here, α is a constant, )(refn-+ is the correction value K ref obtained by the previous execution of step 72. The calculated correction value Krer is the absolute pressure PBA in the intake manifold and the engine rotation speed at this time. RAM31 corresponding to Ne
K ref data map location. It is determined whether the calculated correction value K ref is greater than 0°9 and smaller than 1.1 (step 73), 0.9<
If Kref <1.1, step 65 is immediately executed to calculate the output value TOUT. KrQf≦0.9,
Alternatively, if Krer≧1.1, it is assumed that the magnitude of the correction value K ref is large due to the deviation in the base air-fuel ratio of the carburetor, and the proportional range tsffiPL, which is a unit proportional amount, is corrected in step 74), and then step 74) is performed. 65, the output value Touv is calculated. For example, with the characteristics shown in FIG. 6, the proportional subtraction mPL corresponding to the correction value Krof is stored in the ROM.
30 as a PL data map)
(If ref≦0.9 or Kref≧1.1, the proportional subtraction ff1PL corresponding to the correction value Krcf is searched from the PL data map. If the correction value Kref is 1.1 or more, Since the fuel ratio has shifted to the rich side, the proportional range CutPL is enlarged, and the correction value Krer
If it becomes 0.9 or less, the base air-fuel ratio of the carburetor is shifted to the lean side, so the proportional subtraction IP+- is reduced. In step 53 or 65, the output value TOL
After calculating JT, the output value T is sent to the drive circuit 28.

The IJT is output (step 75).

Note that, as shown in FIG. 6, the proportional subtraction ffi P L is determined in stages with respect to the correction value K ref, but the proportional subtraction ffi P L with respect to the correction value K ref is
P L may be determined continuously. Also RAM
31 is a non-volatile memory whose memory contents do not volatilize even when the engine 5 stops operating, and each K r in the K re4 data map
af is initialized to 1 before use of the device.

The drive circuit 28 detects the current value flowing through the solenoid 9a of the solenoid valve 9 using a current detection resistor, compares the detected current value with the output value ToUT, and turns on and off the drive transistor according to the comparison result. Solenoid 9a
supply current to. Therefore, the current represented by the output value Tour flows through the solenoid 9a, and the solenoid 9 of the solenoid valve 9
An amount of intake secondary air is supplied into the intake manifold 4 in proportion to the current value flowing through the intake manifold 4.

Note that after the time counter A is reset in step 57 and starts counting from the initial value, a predetermined time Δ
If it is determined in step 56 that t1 has not elapsed, step 65 is immediately executed; in this case,
The air-fuel ratio correction value 1OLIT obtained by executing the A/F routine up to the previous time is read out.

In addition, in the above-described embodiments of the present invention, an air-fuel ratio control device equipped with a linear type solenoid valve has been described. 1m valve time T.

LJT (=standard valve opening time TBAsE + correction value tau lower)
The present invention can be applied to an air-fuel ratio control device that calculates the amount and opens the electromagnetic on-off valve by the amount valve time TOUT.

Furthermore, in the embodiment of the present invention described above, correction! II
Although only the proportional subtraction ff1PL has been corrected according to the magnitude of K ref, it is also possible to perform the subtraction ff1PR1 and correct IR as well.

In the air-fuel ratio control method of the present invention, when the correction value representing the error in the reference value is calculated, the unit proportional amount or Since the unit integral amount is corrected, even if the deviation in the base air-fuel ratio of the carburetor becomes large, the air-fuel ratio can be controlled to the target air-fuel ratio with high precision, and the exhaust purification performance can be improved.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing a device to which the air-fuel ratio control method of the present invention is applied, Fig. 2 is a block diagram showing a specific configuration of the control circuit in the device of Fig. 1, and Fig. 3 shows the operation of the CPLJ. (Fig. 4 is a diagram showing the DeAsc data map written to the ROM, and Fig. 5 is a diagram showing the DeAsc data map written to the RAM.)
A diagram showing the ref data map, FIG. 6 shows the correction value K re
FIG. 3 is a diagram showing f-proportional subtraction value PL characteristics. Explanation of symbols of main parts 2... Air cleaner 3... Carburetor 4... Intake manifold 6... Throttle valve 7... Venturi 8 ...Intake secondary air supply passage 9 ...Linear type solenoid valve 10 ...Absolute pressure sensor

Claims (1)

[Claims] In an internal combustion engine equipped with an exhaust component concentration sensor in the exhaust system that generates an output according to the concentration of exhaust components in exhaust gas, a reference value for air-fuel ratio control is set according to multiple engine operating parameters related to engine load, and the reference value is set at a predetermined period. The output value of the exhaust component concentration sensor is compared with the target value at each time, and an air-fuel ratio correction value for proportional control or integral control is obtained according to the comparison result, and the set reference value is used as the air-fuel ratio correction value. An air-fuel ratio control method that determines an output value with respect to a target air-fuel ratio by correcting it accordingly, and calculates a correction value representing an error in the reference value, the method comprising: adjusting the magnitude of the correction value when calculating the correction value; An air-fuel ratio control method, comprising correcting a unit proportional amount or a unit integral amount of the air-fuel ratio correction value accordingly.